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Calclus Level 4 Assessment Question

The question given and my solution are in the image attached. However, I was only allowed to enter an integer as the final answer, so that implies my solution is wrong. Any hints?

EDIT: I found the problem set for my assessment here and the correct answer is the one I worked out, and it is not an integer. That's really quite annoying.

Note by Jordan Barnes
3 years, 7 months ago

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Hi Jordan -

The correct answer to this question is the one you've worked out, and isn't an integer. I'm not sure why it was giving you difficulties before. When I look at your history, it appears this question has been marked correct for you. I'm not sure if this was because you entered a new answer or if Arron edited your results, but I hope this resolves the issue. Daniel Hirschberg · 3 years, 7 months ago

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@Daniel Hirschberg I answered the question on this page to check I had the right answer, but during the assessment I was unable to enter anything other than an integer, so I feel cheated out of my actual level. Jordan Barnes · 3 years, 7 months ago

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Here's what I think happened: this is a problem you'd previously seen on the site before it was placed in the Calculus assessment, but hadn't finished (probably in Calculus practice). As such, you had an already existing attempt on the problem that existed before we switched it over to allow real number answers. Our system loaded the previous attempt on the problem (with the old integer answer), and didn't let you enter a non-integer answer.

This is a pretty ugly edge case, but it has happened to a few people since we made the switch. I apologize for the error and hope you don't hit any more bugs like this. Arron Kau Staff · 3 years, 7 months ago

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@Arron Kau Thank you for the reply, but that's impossible. Last night was the first time I'd used brilliant.org and I did the assessment questions immediately after signing up, without trying any of the other problems on the site. Jordan Barnes · 3 years, 7 months ago

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Here are my thoughts: 1. What if he wants you to round it off? 2. What if z first?

I don't know much, I'm just presenting my views Kenny Lau · 3 years, 7 months ago

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@Kenny Lau Thank you for the reply.

  1. I tried entering the rounded answer, was told it was wrong.
  2. By Fubini's theorem, the order of the integration does not matter as long as the correct limits are applied. I actually did try the integrals in a different order but got the same answer.
Jordan Barnes · 3 years, 7 months ago

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@Jordan Barnes Since the result computed by WolframAlpha is the same as your answer, the only possibility left is that you copied the question wrongly. Kenny Lau · 3 years, 7 months ago

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